In optical network equipment that includes one or more optical network interface cards (ONICs), various schemes for automatic protection switching (APS) provide a secondary interface (i.e., protecting interface) for each of the one or more primary interfaces (i.e., working interfaces) in a particular optical network device. For example, in the event of a failure of a working interface, traffic may be switched from a working interface to its associated protection interface using an APS protocol. As used herein, the term “APS protocol” refers to one or both of the Bellcore GR 253 optical network standard in North America and the International Telecommunications Union (ITU) G.841 optical network standard internationally, the disclosures of which are incorporated by reference herein in their entireties.
A first category of APS configurations includes 1+1 and 1:1 protection schemes for optical network devices. In 1+1 and 1:1 protection configurations, a 1-to-1 ratio exists between working interfaces and protection interfaces. The main difference between 1+1 and 1:1 protection schemes is that 1+1 protection can be configured as both unidirectional and bi-directional protection whereas 1:1 protection can be configured as bi-directional only. A protection system is bidirectional if both local and far end equipment perform traffic switchover together. In other words, if the local equipment has switched over, the far end is required to perform switchover as well. Conversely, a protection system is unidirectional if local and far end equipment can perform switchover independently of each other. Furthermore, there are two important subtypes of 1+1 APS which are discussed below.
1+1 equipment protection (hereinafter, “equipment protection”) requires that working interfaces and protection interfaces be located on different ONICs. Advantages of equipment protection include high reliability because a failure of the working card will not cause a failure of the protection card. However, because equipment protection requires a separate protection card for each working card, the cost is typically expensive.
For example, FIG. 1A illustrates an exemplary conventional equipment protection scheme according to the prior art. Referring to FIG. 1, working card 100 (i.e., W1) includes two working interfaces—Rx1 102 and Tx1 104—for receiving and transmitting synchronous optical networking (SONET) and/or synchronous digital hierarchy (SDH) communications via a fiber optic cable or other suitable transmission medium. Protection card 106 includes two corresponding protecting interfaces 108 and 110, for protecting working interfaces 102 and 104, respectively, in the event of failure. Protection card 106 is located on a separate ONIC from working card 100 and is responsible for handling traffic for working card 100 in the event of a failure of one of receiving interfaces 102 and/or working card 100. Thus, receiving protecting interface 108 on protection card 106 is associated with receiving working interface 102 on working card 100 as indicated by dashed line 112. Similarly, transmitting protecting interface 110 on protection card 106 is associated with transmitting working interface 104 on working card 100 as indicated by dashed line 114.
FIG. 1B illustrates a more detailed schematic view of a conventional 1+1 equipment protection scheme according to the prior art. Referring to FIG. 1B, working card 100 and protecting card 106 may each include O/E converters and data payload processors for processing optical network traffic. For example, cards 100 and 106 may include O/E converters 116 and 118 and payload processors 120 and 122, respectively. Cards 100 and 106 may send and receive optical network traffic via sending and receiving interface pairs 124 and 126, and 128 and 130, respectively. Working card 100 may be connected to protecting card 106 via midplane 132 using a suitable communications bus. Midplane 132 may include one or more bridges and selectors for directing traffic between working card 100 and protecting card 106. For example, in the configuration shown in FIG. 1B, bridge 134 is a permanent bridge such that outbound communications from protecting card is always tied to protecting card 106. Relatedly, selector 136 is shown in a position that data received from working card 100 is allowed to pass through midplane 132 whereas data received from protecting card 106 is not because working card 100 is operational and has not experienced a failure event or condition requiring that switchover be performed.
In contrast to equipment protection, which requires that the working and protection interfaces be located on different ONICs, 1+1 facility protection (hereinafter, facility protection”) requires that the working and protection interfaces be located on the same ONIC. FIG. 2 illustrates an exemplary facility protection scheme. Referring to FIG. 2, ONIC 200 includes a first pair of working optical fibers 202 and 204 for receiving and transmitting information, respectively. Also located on the same ONIC 200, corresponding protecting optical interfaces 206 and 208 provide backup interfaces for working interfaces 202 and 204, respectively. Again, the 1-to-1 relationship between working and protection interfaces is indicated by dashed lines 210 and 212 representing associations between receiving interfaces 202 and 206 and transmitting interfaces 204 and 208, respectively.
Advantages of facility protection include that it is cheaper to implement than equipment protection because fewer cards and midplane slots are required as compared to equipment protection. However, facility protection is less reliable than equipment protection because if a ONIC fails, both working and protection interfaces may be affected and, as a result, traffic may be lost.
In order to address the inherent deficiencies associated with conventional 1+1 protection, conventional 1:N (aka, 1-to-N) protection may be used. Conventional 1:N protection provisions one redundant interface for each of N working interfaces, where N is an arbitrary, user-determined value that may be dictated by the particular device configuration and traffic demands (i.e., 1:1 is just a special case of 1:N). As used herein, 1:N and 1-to-N are intended to refer to the same APS configuration (i.e., one protecting interface protecting N working interfaces), where 1:N protection for an optical network is always bidirectional protection.
FIG. 3 illustrates an exemplary conventional 1:N protection scheme. Referring to FIG. 3, a plurality of working ONICs 300, 302 and 304 may each contain receiving optical interfaces 306, 308, and 310, respectively, as well as transmitting optical interfaces 312, 314, and 316, respectively. Protection card 318 may include a single receiving protection interface 320 and a single transmitting protection interface 322. Receiving protection interface 320 may protect interfaces 306, 308, and 310 and transmitting protection interface 322 may protect interfaces 312, 314, and 316. These associations are indicated by dashed lines 324 and 326, respectively. Thus, a single protection interface (e.g., receiving protection interface 320) may protect N (e.g., three) working interfaces (e.g., interfaces 306, 308, and 310).
FIG. 4 is a schematic diagram of an exemplary conventional 1:N APS configuration. Referring to FIG. 4, N working cards and their associated protecting card may each include an optical/electrical (O/E) converter for converting between optical, which may be used for transmission between local and far end equipment, and electrical signals, which may be used internally by each card. For example, working cards 300, 302, and 304 and protecting card 318 may include O/E converters 400, 402, 404, and 406, respectively. Specifically, O/E converter 400 may convert an electrical signal to an optical signal (e.g., SONET/SDH) for transmission using outbound optical interface 408 or, alternatively, may convert an optical signal to an electrical signal that is received on inbound optical interface 410. Likewise, O/E converters 402, 404, and 406 may convert between signals transmitted or received on optical links 412, 414, 416, 418, 420, and 422 as indicated in FIG. 4. Each of cards 300-304 and 318 may also include a digital payload processor for processing signals received from O/E converters 400-406, respectively. For example, cards 300-304 and 318 may include payload processors 408, 410, 412, and 414, respectively, which may include any suitable hardware for executing instructions stored on a computer readable medium.
Each of working cards 300-304 and protecting card 318 may be connected to a midplane or backplane for communicating between them. For example, midplane 416 may include multiple internal communications interfaces (e.g., PCI slots) for connecting together cards 300-304 and 318. Midplane 416 may also include one or more systems for controlling which working card is connected to the protecting card, thereby determining which working card may currently be switched over to the protecting card.
As may be appreciated, unidirectional APS is possible if outbound data is permanently bridged to the working and protecting cards at both local and far end equipment. A permanent bridge allows the far end to receive identical data on its working and protecting cards. Thus, if a switchover is needed by the far end, it only needs to select the inbound data from its standby card and the far end switchover does not require the local end to perform any action. Likewise, since the far end has permanent bridge for its outbound data, local switchover is also independent of the far end equipment. However, a conventional 1:N optical APS system may only work in bi-directional fashion because a permanent bridge is not possible because the protecting card does not know beforehand which working card to bridge traffic for.
The APS system shown in FIG. 4 is in “standby mode” where no switchover is being performed and therefore bridge controllers 418-422 are each in an open position. As a result, outbound data is not received by protecting card 318. If traffic switchover is desired for working card 302, for example, then bridge controller 420 will close, and selector 426 will switch to the inbound interface of protecting card 318. As may be appreciated from FIG. 4, working cards 300-304 and protecting card 318 are built exactly the same and traffic switchover is performed completely on the midplane.
An advantage of conventional 1:N protection is that it is more reliable than facility protection because working and protecting interfaces are located on separate cards. Conventional 1:N protection is also cheaper than equipment protection because fewer protection cards are required to protect multiple working cards (i.e., N>1).
However, 1:N protection is typically complex to implement because it requires synchronized switchover actions on both local and remote optical network equipment. Specifically, in order to perform synchronized switchover, the complex APS protocols described above requiring strict compliance must be used. Due to the complexity associated with conventional 1:N protection schemes, few optical network equipment vendors support 1:N protection and its commercial deployment is virtually non-existent.
Accordingly, in light of these difficulties, a need exists for improved methods, systems, and computer readable media for automatic protection switching for optical network interface equipment.